Mac mini monitor flickering again

I have a Mac mini (M1) and Dell 2721QS connected with an HDMI cable. It worked great out of the box and had no problems. Then, some time ago, the screen began flickering. I believe I set it back to defaults and it began working fine (1920x1080 and 60Hz). It was fine for many months but now the flickering has resumed... and I don't have another trick to try. Can you help? Thank you.